The following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art.
U.S. Pat. No. 5,177,468 (Baldwin et al.) describes a conduit liner monitor that allows for the non-destructive determination of the status of a liner disposed within a conduit. The conduit may, for example, be an elbow, valve, pipe. At least one wire is disposed within the liner in an area of concern. The wire is connected to a receptacle located on the conduit. A status display plugs into the receptacle and checks the continuity of the wire. If a wire is broken, this information is displayed, indicating a potential problem with the liner.
U.S. Pat. No. 6,386,237 (Chevalier et al.) describes an abrasive material transport hose with wear detecting sensors. The useful life of an abrasive material transport hose can be maximized if the hose is repositioned at the first signs of internal wear. This is accomplished by disposing at least two wear sensing elements, each at a specified distance from the inwardmost surface of the inner tube, and each monitoring a condition indicative of wear of the hose at its specified distance from the inwardmost surface of the inner tube. When the innermost wear sensing element implies wear, the hose can be repositioned to extend the useful life until the outermost wear sensing element indicates wear requiring replacement of the hose.